I use the Contivity client every day (I work for Nortel ) and with version 4.87 and NAT transversal it works just fine. It also requires that the contivity server have NAT transversal enabled. If you cannot do this, just hand the Vonage box off one of the router ports by itself and you will be ok too. This is what I used to do. You should make sure that your router supports IPSec VPN access too because the older versions of the Linksys software did not do this properly.